BAGHDAD, Iraq — Gunmen kidnapped a Lebanese-American businessman — the second U.S. citizen seized this week in Baghdad — and videotape Wednesday showed the beheadings of three Iraqi National Guardsmen and an Iraqi officer.

Elsewhere, a U.S. soldier was killed and another wounded in a roadside bombing 12 miles south of the capital. A suicide driver detonated his vehicle at a checkpoint near Baghdad airport, injuring nine Iraqis and prompting U.S. troops to close the main route into the city for hours.

U.S. jets were in action again late Wednesday over Fallujah, striking insurgent targets in the northeastern and southern parts of the city, where American forces are said to be gearing up for a major assault.

Residents reported fierce exchanges of fire after midnight on the edge of the city.

Gunmen killed a senior oil ministry official, Hussein Ali al-Fattal, after he left his house Wednesday in the Yarmouk district of western Baghdad, police said. Al-Fattal was the general manager of a state-owned company that distributes petroleum byproducts.

Al-Jazeera television broadcast a threat by an unspecified armed group to strike oil installations and government buildings if the Americans launch an all-out assault on Fallujah.

The report was accompanied by a videotape showing about 20 armed men brandishing various weapons including a truck-mounted machine gun.

The violence served as a grim reminder of Iraq’s rapidly deteriorating security situation, which President Bush must address now that he has won his long electoral contest against Sen. John Kerry, who conceded defeat Wednesday.

Radim Sadeq, an American of Lebanese origin who worked for a mobile phone company, was grabbed about midnight Tuesday when he answered the door of his home in Baghdad’s upscale Mansour neighborhood, officials said. No group claimed responsibility.

It was the second abduction this week in Mansour, where many foreign companies are based. On Monday, gunmen stormed the two-story compound of a Saudi company, abducting six people: an unidentified American, a Nepalese, a Filipino and three Iraqis, two of whom were later released. No claim has been made for the kidnappings.

More than 170 foreigners have been kidnapped and more than 30 of them killed in Iraq since Saddam Hussein’s regime fell in April 2003.

At least six of the foreigners were beheaded by followers of Abu Musab al-Zarqawi, a Jordanian militant who has sworn allegiance to al-Qaida.

As the wave of abductions continues, another militant group, the Ansar al-Sunnah Army, posted a videotape on a Web site Wednesday showing the beheading of a man it said was an Iraqi army major captured in the northern city of Mosul.

A statement by the group called Maj. Hussein Shanoun an “apostate” and said he confessed to taking part in attacks against insurgents on orders of the Americans.

Just before his death, the victim was shown warning Iraqi soldiers and police against “dealing with the infidel troops,” meaning the Americans.

In another video, aired Wednesday on Al-Jazeera, a previously unknown group calling itself the Brigades of Iraq’s Honorables said it beheaded three Iraqi National Guardsmen, accusing them of spying for the Americans.

The broadcast showed three men holding up what appeared to be army identification cards sitting in front of a hooded man who read a statement.

The video also showed the beheading of the three men, but the network declined to air that part of the tape, the Al-Jazeera newscaster said.

In Jordan, a government spokeswoman said four Jordanian drivers were kidnapped in Iraq and two others were shot at by unknown assailants. The spokeswoman, Asma Khader, gave no details of the abductions but said two other Jordanians came under fire in the Ramadi area in central Iraq — a stronghold of Sunni Muslim militants.

Insurgents have stepped up attacks on Iraq’s U.S.-trained security forces, who the Americans hope will assume greater responsibility to enable Washington to begin drawing down its forces — now at their highest levels since the summer of 2003.

More than 85 percent of the estimated 165,700 multinational troops here are Americans, despite U.S. efforts to encourage other countries to share the burden of securing and rebuilding Iraq.

On Wednesday, Hungary’s prime minister said the country would withdraw its 300 non-combat troops by the end of March. Hungary had agreed to extend their deployment from an original deadline of Dec. 31 so they could help maintain security during elections in January.

Prime Minister Ferenc Gyurcsany said a further extension after the election would be “impossible.”

Elsewhere, attackers fired a mortar round Wednesday at an Iraqi National Guard checkpoint in Najaf’s old city, injuring two soldiers, Lt. Haidar Hussein said. It was the first such attack in the center of the Shiite holy city since a peace agreement last August ended weeks of fighting between U.S. troops and Shiite militiamen.

In Samarra, 60 miles north of Baghdad, residents said U.S. soldiers clashed with gunmen Wednesday in the city center. Four Iraqis were killed and two injured, said Ahmed Jadour of the Samarra General Hospital.

A statement distributed Wednesday in Samarra warned Iraqis against turning in weapons to the Americans.

“The occupier is thinking of a new way to corrupt the morals of the honorable Muslims by paying huge sums of money to buy weapons that are not worth anything compared to his destructive weapons,” the statement said. “We will not allow any person who helps the infidels and turns over his weapons to the enemy to live among honorable people.”

To the west of the capital, U.S. forces are preparing for a major offensive against Fallujah and other Sunni militant strongholds in hopes of curbing the insurgency ahead of January’s election.

The late night attacks on Fallujah followed air raids earlier in the day that struck an insurgent command post; a weapons cache site in the city was destroyed late Tuesday, the U.S. military said.

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